Download Lecture 17: Sensation

Lecture 17: Sensation
M/O Chapter 19
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Trace the path of light as it passes through the eye to the retina.
Describe the path of a nerve impulse from the retina to various parts of the brain.
Relate changes in the anatomy of the eye to changes in vision.
Describe the path of nerve impulses from the olfactory receptors to various parts of the brain.
Identify the location and structure of taste buds.
Describe the path of nerve impulses from the gustatory receptors to various parts of the brain.
Trace the path of sound conduction from the auricle to the fluids of the inner ear.
Describe the path of nerve impulses from the cochlea to the various parts of the brain.
Classifications of sensory information
1. General sensation relies on sensory receptors that are widely distributed throughout the body.
A. Usually. general sensory receptors are the dendrites of a sensory neuron.
B. There are a diverse set of different kinds of general receptors, including free dendrites (pain, hair movement, light touch)
and encapsulated dendrites (regular touch, pressure)
2. Special senses come from specific receptor ORGANS that transmit the sensory information to the brain.
A. Special sense organs usually have specialized receptor CELLS that receive information, and then pass the information to
sensory neurons.
B. The receptor cells usually are concentrated in a specialized epithelium, or sensory organ.
Taste (aka gustatory system): Anatomy and neural pathways
Check out a slide of the tongue here: http://141.214.65.171/Histology/Digestive%20System/Oral%20Region/117_HISTO_20X.svs/
view.apml?
Taste receptors are found embedded in the mucous membrane of in the tongue. They pass information to the two cranial nerves
involved in taste: CN VII (anterior 2/3) and CN IX (posterior 1/3) (See fig 19.8 in M/O)
Smell (aka olfactory system): Anatomy and neural pathways
Smell receptors are actual dendrites found on the neurons that synapse with neurons in the olfactory tract (CN I).
Hearing: Anatomy
Complex anatomy allows transfer of mechanical energy (sound waves in the air) to a nerve impulse that is interpreted as SOUND.
1. External ear
A. Sound waves are “caught” by the pinna, travel through the ear canal, and run into the tympanic membrane and VIBRATE
the membrane.
2. Middle ear:
A. Middle ear bones (malleus, incus, stapes) are attached at one end to the tympanic membrane and at the other end to the oval
window, a thin membrane separating the middle and inner ear
B. These bones enable an increase in the FORCE applied by the original sound wave to the oval window by a factor of 22
3. Inner ear
A. Cochlea and semicircular canals
B. Sound waves travel through the fluid filled cochlea where non-neural receptor cells (hair cells- about 16000 of them) are
stimulated and transmit the information to the brain.
C. Semicircular canals contain fluid that detects rotational acceleration as fluid inside sloshes
i. Utricles and sacules contain little rocks that trigger receptor cells when you change your position…
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Hearing: Neural Pathways
See Fig 19.30
Vision: Anatomy
The eye is a complex receptor organ containing receptor cells that are sensitive to light. It arises from extensions of diencephalon,
and as such is literally brain tissue. The eye is composed of 3 layers, which are called tunics.
1. Fibrous tunic: the outermost layer, made of CT.
A. Extension of the dura mater!
B. Anterior 1/6: Cornea
i. This translucent layer lets light in and bends the light to help it focus on the retina.
C. Posterior 5/6: Sclera
i. This tough, opaque, white layer protects the contents of the eye. The 6 muscles that move the eyeball within the socket
attach to the sclera.
2. Vascular tunic
A. Extension of the arachnoid/pia mater
B. Anterior 1/3:
i. Iris: The pigmented part of the eye
a. Pupil: A hole in the iris
b. Contains 2 layers of smooth muscle that control pupil diameter via VM innervation.
ii. Ciliary body
a. These structures hold attach to the lens via the suspensory ligaments
b. Contains muscles that change the shape of the lens, allowing the eye to focus on near objects, then focus on far
away objects too.
c. Also contains cells that produce the aqueous humor, which is the fluid that fills the anterior 1/3 of the eye.
C. Posterior 2/3
i. Choroid
a. This connective tissue layer links the outer protective fibrous tunic to the inner, functional layer of the eye.
b. Nourishes the retina
c. Absorbs stray light that might bounce around the eyeball
3. Retina
A. This is the innermost optic cup
B. Anterior 1/3: Absent!
C. Posterior 2/3
i. Pigmented retina
a. Single layer of cells that provides vitamin A to the neural retina.
b. Also helps absorb extra light
c. Sandwiched between neural retina and choroid
ii. Neural retina
a. Innermost layer of the eye
b. Contains all the photoreceptor cells (like cones and rods)
c. Information gathered by these photoreceptor cells is carried to the occipital lobe via the optic nerve (CN II).
Vision: Neural Pathways
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Lab 17: Sensation(al!)
M&O Ch.11 (eye muscles), Ch. 19 (eye gross anatomy); M&O 19 (ear gross anatomy)
E Ch. 11, Ch. 15, Ch. 20 (selected portions on taste, smell, vision) E Ch. 20 (selected portions on hearing)
I. Cow Eye Dissection
(see M&O Fig. 19.12 and 19.13 for guidance)
1. From the outside of the eye, identify the optic nerve, cornea, sclera, iris, and pupil.
2. Now using your scissors or a scalpel cut the eye into equal halves (but try not to cut through the lens). As you do so, a jelly-like
substance should plop out of the posterior cavity into your dissecting tray - this is the vitreous body (aka vitreous humor).
3. On the inside of the posterior cavity of the eye identify the neural retina (whitish membrane that usually collapses) and
pigmented retina.
4. The optic disc is where the axons from the neural retina run out through the optic nerve. Look carefully on the neural retina to
try and find the pit of the macula lutea – this is the fovea (fovea centralis).
A. What is the significance of the fovea for vision?
5. Note the black choroid, which includes a blue opalescent layer of highly reflective tissue in the cow eye called the tapetum
lucidum. (The tapetum lucidum reflects light, producing eyeshine, and contributes to superior night vision)
6. Observe the lens anteriorly, attached by suspensory ligaments to the ciliary body.
7. Just posterior to the ciliary body note the ora serrata, the anterior border of the photoreceptive retina.
8. Now remove the lens, so that you can see into the anterior cavity, and examine the inner surface of the iris and pupil. This space
is filled with aqueous humor, which is produced by the ciliary bodies.
9. Identify the fibrous tunic, vascular tunic, and retina.
II. Eye Model
On the eye model, identify the following accessory ocular structures. Also identify the as many of the previously described structures
as possible.
1. You are responsible for the innervation and action of each of the following extrinsic eye muscles (see M/O Fig 11.4).
Muscle (C-level)
superior rectus
inferior rectus
medial rectus
lateral rectus
superior oblique
inferior oblique
levator palpebrae superior
Innervation (B-level)
Action (eye “looks”) (A-level)
2. Also identify the following structures that are a part of the lacrimal apparatus (see M&O Fig. 19.11)
A. lacrimal gland (in model, stuck onto eyeball)
B. superior lacrimal canaliculus
C. inferior lacrimal canaliculus
D. lacrimal puncta
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III. Histology
Identify the listed structures on each of the following slides.
1. Taste Buds (HK 2-26)
A. lingual epithelium
B. taste bud
C. taste pore
D. supporting cells...note in the slide you can’t tell the difference.
IV. Ear Model
On the ear model, identify the following structures. M&O Figs. 19.21 and 19.22 should prove useful.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
pinna
external auditory meatus (review its location on the skull)
tympanic cavity
auditory tube (aka eustachian or pharyngotympanic tube --look for this on the half head as well)
semicircular canals
internal acoustic meatus (review its location on the skull)
tympanic membrane
cochlea
facial nerve
vestibulocochlear nerve
A. vestibular nerve
B. cochlear nerve
V. Isolated Ear Bones (in resin block)
1. Examine the isolated bones. Identify each bone.
A. malleus
B. incus
C. stapes
Bio 6: Human Anatomy
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Spring 2014: Riggs
External Brain 17: Sensation
80.
81.
82.
83.
84.
85.
86.
87.
Trace the path of light as it passes through the eye to the retina.
Describe the path of a nerve impulse from the retina to various parts of the brain.
Relate changes in the anatomy of the eye to changes in vision.
Describe the path of nerve impulses from the olfactory receptors to various parts of the brain.
Identify the location and structure of taste buds.
Describe the path of nerve impulses from the gustatory receptors to various parts of the brain.
Trace the path of sound conduction from the auricle to the fluids of the inner ear.
Describe the path of nerve impulses from the cochlea to the various parts of the brain.
Your Task
1. Label images or DRAW pictures that include ALL required lab structures.
2. Which ear bone attaches to the tympanic membrane?
3. Which ear bone inserts into the oval window?
4. What passes through the internal acoustic meatus?
5. What two spaces does the tympanic membrane separate?
6. What two spaces does the eustachian tube connect?
7. Describe the neural pathways that cause pupil constriction. What kinds of muscles are involved?
8. Describe the neural pathways that cause pupil dilation. What kinds of muscles are involved?
9. Summarize the pathway by which information is delivered from the tongue to the brain.
10. Summarize the pathway by which information is delivered from the eyes to the brain.
11. Summarize the pathway by which information is delivered from the nose to the brain.
12. Summarize the pathway by which information is delivered from the ears to the brain.
Bio 6: Human Anatomy
79
Spring 2014: Riggs